Many customers would like to customize the ITS login page, so that it fits to their corporate standards. If you search information about how to customize the login page either in ITS 6.20 or with SAP Netweaver 2004/2004s/2007 with integrated ITS read this tutorial.
If you want to customize ITS system templates (and login page is one of these), ITS provides an easy way to do this. The system folder below SAP/ITS/6.20/<YOUR_INSTANCE_NAME>/templates contains two folders dm and pm. dm stands for development mode, pm for production mode. By default ITS stores the system templates in the dm folder. If you want to customize one of the ITS system templates just copy it to the pm folder. There you can modify it as you like. When ITS looks for a system template, it will at first look in pm. If it finds the template there it will use it. Otherwise it will look in dm. To modify the login page just copy the login.html from dm to pm and change it according to your requirement. From now on ITS will use this template for login. If you want to use a service specific login page create a template with the name login.html and store it beside your other service templates. When a user wants to login to this service, ITS will use this template for the login screen. For ITSmobile ITS 6.20 of patchlevel 27 or higher contains a special login page for ITSmobile which fits to the small display of mobile devices. The name is of the template is loginmobile.html. If you want to modify the mobile login page proceed as described above and copy loginmobile.html to pm or to your service directory.
With SAP Netweaver 2004 ITS is part of the SAP kernel. The login page is therefore no longer a functionality of ITS but of the Web Application Server (WAS). By default ITS Services uses the standard system login pages that WAS provides. You can customize in transaction SICF what login procedure should be used and which fields should be available on system login page. This can be done global or per service. The documentation on the SAP help portal contains information how this can be done. It is even possible to create an own login page by inheriting an own login class from CL_ICF_SYSTEM_LOGIN. You can find detailed information about how to do this on the SAP help portal System Logon. For mobile devices Netweaver provides the CL_MOBILE_SYSTEM_LOGIN class.